Exception when trying to convert HeartRate from HealthKitStore

Question

I am working on my first iPhone App: a simple app showing the heartRate results from HealthKit in a nice way. My first step is to show the results as a raw text. But unfortunately I'm getting an exception at the following line, telling me: "thread 1 signal SIGABRT". Does someone know, what I did wrong and hint me in a direction?

double usersBeatsPerMinute = [quantity doubleValueForUnit:[HKUnit countUnit]];

The rest of the code looks like this:

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
// Set up an HKHealthStore, asking the user for read/write permissions. The profile view controller is the
// first view controller that's shown to the user, so we'll ask for all of the desired HealthKit permissions now.
// In your own app, you should consider requesting permissions the first time a user wants to interact with
// HealthKit data.
if ([HKHealthStore isHealthDataAvailable]) {
    NSSet *writeDataTypes = [self dataTypesToWrite];
    NSSet *readDataTypes = [self dataTypesToRead];

    [self.healthStore requestAuthorizationToShareTypes:writeDataTypes readTypes:readDataTypes completion:^(BOOL success, NSError *error) {
        if (!success) {
            NSLog(@"You didn't allow HealthKit to access these read/write data types. In your app, try to handle this error gracefully when a user decides not to provide access. The error was: %@. If you're using a simulator, try it on a device.", error);

            return;
        }

    }];
}

HKQuantityType *weightType = [HKQuantityType quantityTypeForIdentifier:HKQuantityTypeIdentifierHeartRate];

// Since we are interested in retrieving the user's latest sample
// we sort the samples in descending order by end date
// and set the limit to 1
// We are not filtering the data, and so the predicate is set to nil.
NSSortDescriptor *timeSortDescriptor = [[NSSortDescriptor alloc] initWithKey:HKSampleSortIdentifierEndDate ascending:NO];

// construct the query & since we are not filtering the data the predicate is set to nil
HKSampleQuery *query = [[HKSampleQuery alloc] initWithSampleType:weightType predicate:nil limit:1 sortDescriptors:@[timeSortDescriptor] resultsHandler:^(HKSampleQuery *query, NSArray *results, NSError *error) {

    // if there is a data point, dispatch to the main queue
    if (results) {
        dispatch_async(dispatch_get_main_queue(), ^{
            HKQuantitySample *quantitySample = results.firstObject;

            // pull out the quantity from the sample
            HKQuantity *quantity = quantitySample.quantity;

            double usersBeatsPerMinute = [quantity doubleValueForUnit:[HKUnit countUnit]];
            _HeartRateResults.text = [NSString stringWithFormat:@"%@ lbs", [NSNumberFormatter localizedStringFromNumber:@(usersBeatsPerMinute) numberStyle:NSNumberFormatterNoStyle]];
        });
    }
}];

// do not forget to execute the query after its constructed
[_healthStore executeQuery:query];}

Answer 1

There was a comment in the documentation ("These samples use count/time units") I didn't quite understand, so I did a little searching and tried it out and was able to get a value I manually put into the Health app using this:

double rate = [mostRecentQuantity doubleValueForUnit:[[HKUnit countUnit] unitDividedByUnit:[HKUnit minuteUnit]]];

I haven't seen unitDividedByUnit before. Here's the article I pulled it from.